In golf balls commercially selling, there are solid golf balls such as two-piece golf ball, three-piece golf ball and the like, and thread wound golf balls. Recently, the solid golf balls, of which flight distance can be improved while maintaining soft and good shot feel at the time of hitting as good as the conventional thread wound golf ball, generally occupy the greater part of the golf ball market. Multi-piece golf balls represented by three-piece golf ball have good shot feel while maintaining excellent flight performance, because they can vary hardness distribution, when compared with the two-piece golf ball.
Launch angle and backspin of golf ball have a great effect on trajectory of the golf ball hit by a golf club. The hit golf ball having large launch angle tends to have high trajectory, and the hit golf ball having small launch angle tends to have low trajectory. Since the backspin provides lift to the hit golf ball, the hit golf ball having large backspin amount tends to have high trajectory, and the hit golf ball having small backspin amount tends to have low trajectory. Performance requirements of golf balls from golfers include flight distance, shot feel, controllability and the like. When golfers use a golf club, particularly wood club (such as a driver), long iron club, middle iron club and the like, the flight distance is an important performance requirement.
In order to improve the flight distance when hit by a golf club such as a wood club, it is required for the hit golf ball to have high trajectory and long flight duration to a certain extent as well known. The hit golf ball having large launch angle and large backspin amount has high trajectory as described above, but the hit golf ball having too large backspin amount tends to have short flight distance. It is reason that kinetic energy is consumed by backspin, and that force applied such that the hit golf ball is pulled backward occurs by the lift until the golf ball reaches the highest point of the trajectory because the lift is applied perpendicular to the flight direction of the golf ball. Therefore, golf ball, of which the backspin amount is not very large and high trajectory is accomplished by high launch angle, has long flight distance when hit by a golf club, such as a wood club.
The shot feel is also an important performance requirement. When the shot feel is too hard, the golf ball has too short contact time with a golf club even if the backspin amount is small, and golfer can not easily hit the golf ball. On the other hand, when the shot feel is too soft, golfer feels that the golf ball has poor shot feel such that rebound characteristics are poor.
Based on the above knowledge, there has been many developments of golf ball having long flight distance accomplished by low backspin amount and high launch angle at the time of hitting, and good shot feel, from the viewpoint of formulation of the material and structure of the golf ball (Japanese Patent Kokai Publication Nos. 38238/1997, 239033/2002 and the like).
In Japanese Patent Kokai Publication No. 38238/1997, a golf ball comprising a core and a cover covering the core is disclosed. The cover has a two-layer structure composed of an outer cover and an inner cover, the inner cover is prepared from a resin composition having a flexural modulus of 5,000 to 12,000 kgf/cm2 at 23° C. and a of 50%, and comprising a polyamide resin having a flexural modulus of 6,000 to 30,000 kgf/cm2 at 23° C. and a relative humidity of 50% and a thermoplastic elastomer having a JIS-A hardness of 30 to 98, in a weight ratio of polyamide resin:thermoplastic elastomer within the range of 95:5 to 50:50.
In Japanese Patent Kokai Publication No. 239033/2002, a multi-piece solid golf ball comprising a core, an inner cover formed on the core and an outer cover covering the inner cover is disclosed. The inner cover has a Shore D hardness of 30 to 62, and is formed from an inner cover composition comprising                (a) 50 to 95 parts by weight of ethylene-(meth)acrylic acid copolymer ionomer resin, and        (b) 5 to 50 parts by weight of thermoplastic elastomer formed from a polymer alloy of an olefin with a block copolymer having styrene block, based on 100 parts by weight of a base resin, and the block copolymer having styrene block is selected from the group consisting of styrene-butadiene-styrene block copolymer (SBS), hydrogenation product of SBS, styrene-isoprene-styrene block copolymer (SIS), hydrogenation product of SIS, styrene-isoprene-butadiene-styrene block copolymer (SIBS), and hydrogenation product of SIBS,        the outer cover is formed from an outer cover composition comprising ionomer resin as a main component, and has a Shore D hardness of 58 to 68, and        the hardness of the outer cover is higher than that of the inner cover.        
However, it has been required to provide golf balls, of which the flight distance and shot feel are improved still more. Therefore, there has been no golf ball, which is sufficient to the balance between excellent flight performance by accomplishing small backspin amount and high launch angle at the time of hitting, and good shot feel at the time of hitting.